Network Design with WLAN, VOIP, & VPN

I need to design a network for 20 users on site and 10 users via VPN. Those 20 users are connected on WLAN. They also use VOIP application. I need to design a converged network and provide detail design.

First of all i should say i know only the theory. I thought of designing with DMZ. But after considering some answers here i'm confused. Now i think there is no need for DMZ. Could some one suggest a better view.

My design would be,

ISP router --> VPN and Firewall ---> LAN

LAN with both wired domain for servers and wireless domain.

I just read about Wireless LAN Controller(WLC) and considering to use it though i dont have a clear idea.

Ya. Of course it's homework. I haven't mentioned a real scenario. So that i said i know about the components and need a design. How did u all learn then ? Born with the knowledge !!! I need suggestion from people who have experienced. Not some bulls--- comments to fill the space.... :(

The quiz states wireless-based voice/data network. So i have to design in that way.....I need a better design. You can presume i have a fair knowledge on wireless, wired network and components. I have another problem with implementing VOIP over wireless. Which would be the best out of 802.11 a,b or g (hope not b ) ?

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